A seizure may be characterized as abnormal or excessive synchronous activity in the brain. At the beginning of a seizure, neurons in the brain may begin to fire at a particular location. As the seizure progresses, this firing of neurons may spread across the brain, and in some cases, many areas of the brain may become engulfed in this activity. Seizure activity in the brain may cause the brain to send electrical signals through the peripheral nervous system to different muscles. For example, an electrical signal may originate in the central nervous system and initiate the propagation of an electrical signal through motor neurons. A motor neuron may, for example, communicate with a muscle through interaction with the motor end plate of a muscle fiber; thereby initiating an action potential and depolarization of muscle cells within a given motor unit. Depolarization typically results from the coordinated flow of ions, e.g., sodium and potassium cations, through channels within a muscle cell membrane. That is, changes in states of ion channels initiate a change in the permeability of a cell membrane, and subsequent redistribution of charged ions. Current flow through muscle cells may initiate a corresponding flow in the tissue above the muscle and thus an electrical signature at the surface of the skin.
Techniques designed for studying and monitoring seizures have typically relied upon electroencephalography (EEG), which characterizes electrical signals using electrodes attached to the scalp or head region of a seizure prone individual, or seizure patient. EEG electrodes may be positioned so as to measure such activity, that is, electrical activity originating from neuronal tissue. Compared to EEG, electromyography (EMG) is a little-used technique in which an electrode may be placed on or near the skin, over a muscle, to detect an electrical current or change in electric potential in response to redistribution of ions within muscle fibers.
Detecting an epileptic seizure using electroencephalography (EEG) typically requires attaching many electrodes and associated wires to the head and using amplifiers to monitor brainwave activity. The multiple EEG electrodes may be very cumbersome and generally require some technical expertise to apply and monitor. Furthermore, confirming a seizure requires observation in an environment provided with video monitors and video recording equipment. Unless used in a staffed clinical environment, such equipment is frequently not intended to determine if a seizure is in progress but rather provide a historical record of the seizure after the incident. Such equipment is usually meant for hospital-like environments where a video camera recording or caregiver's observation may provide corroboration of the seizure, and is typically used as part of a more intensive care regimen such as a hospital stay for patients who experience multiple seizures. A hospital stay may be required for diagnostic purposes or to stabilize a patient until suitable medication can be administered. Upon discharge from the hospital, a patient may be sent home with little further monitoring. However, at any time after being sent home the person may experience another seizure, perhaps fatal.
A patient should in some cases be monitored at home for some length of time in case another seizure should occur. Seizures with motor manifestations may have patterns of muscle activity that include rhythmic contractions of some, most, or all of the muscles of the body. A seizure could, for example, result in Sudden Unexplained Death in Epilepsy (SUDEP). The underlying causes of SUDEP are not well understood; however, some possible mechanisms causing SUDEP may include tonic activation of the diaphragm muscle so as to prevent breathing, neurogenic pulmonary edema, asystole, and other cardiac dysrhythmia. If a sleeping person experiences a seizure involving those conditions, then caregivers may not be aware that the seizure is occurring, and thus be unable to render timely aid.
While there presently exist ambulatory devices for diagnosis of seizures, they are EEG-based and are generally not designed or suitable for long-term home use or daily wearability. Other seizure alerting systems may operate by detecting motion of the body, usually the extremities. Such systems may generally operate on the assumption that while suffering a seizure, a person will move erratically and violently. For example, accelerometers may be used to detect violent extremity movements. However, depending upon the type of seizure, this assumption may or may not be true. Electrical signals sent from the brain during the seizure are frequently transmitted to many muscles simultaneously, which may result in muscles fighting each other and effectively canceling out violent movement. In other words, the muscles may work to make the person rigid rather than cause actual violent movement. Thus, the seizure may not be consistently detected with accelerometer-based detectors.
Accordingly, there is a need for an epileptic seizure detection method and apparatus that can be used in a non-institutional or institutional environment without many of the cumbersome electrodes to the head or extremities. Such an apparatus may be minimally intrusive, minimally interfere with daily activities and be comfortably used while sleeping. There is also a need for an epileptic seizure detection method and apparatus that accurately detects a seizure with motor manifestations and may alert one or more local and/or remote sites of the presence of a seizure. Furthermore, there is a need for an epileptic seizure detection method and apparatus that may be used in a home setting and which may provide robust seizure detection, even in the absence of violent motion, and which may be personalizable, e.g., capable of being tailored for an individual or specific population demographic.